trace_processor: add support for sched_process_exit events

This allows for identifying when threads are ending in traces associated
with startup.

Change-Id: I05c3b9479b927b7dd0d287f7ac4840632c634503
Bug: 133848691
diff --git a/src/trace_processor/trace_storage.h b/src/trace_processor/trace_storage.h
index 4ea1928..f757e25 100644
--- a/src/trace_processor/trace_storage.h
+++ b/src/trace_processor/trace_storage.h
@@ -105,6 +105,7 @@
   struct Thread {
     explicit Thread(uint32_t t) : tid(t) {}
     int64_t start_ns = 0;
+    int64_t end_ns = 0;
     StringId name_id = 0;
     base::Optional<UniquePid> upid;
     uint32_t tid = 0;